Citrobacter rodentium Induces Tissue-Resident Memory CD4⁺ T Cells

Area of Science:

• Immunology
• Microbiology
• Cellular Biology

Background:

• Tissue-resident memory T cells (T_RM) are vital for long-term immunity and tissue defense against pathogens.
• While CD8⁺ T_RM cell biology is established, CD4⁺ T_RM cell regulation and function remain less understood.
• Citrobacter rodentium infection is known to induce IL-17A⁺ and IL-22⁺ CD4⁺ T cells, suggesting a potential role in T_RM cell induction.

Purpose of the Study:

• To investigate whether Citrobacter rodentium infection induces CD4⁺ T_RM cells.
• To characterize the properties and functions of these induced CD4⁺ T_RM cells.
• To determine the role of CD4⁺ T_RM cells in host defense against secondary infections.

Main Methods:

• Induction of CD4⁺ T cells in response to Citrobacter rodentium infection.
• Assessment of tissue residency, antigen specificity, and cytokine production (IL-17A, IL-22) of CD4⁺ T cells.
• Utilized FTY720 to differentiate between circulating and tissue-resident T cells.
• Evaluated host defense during secondary infection.

Main Results:

• Citrobacter rodentium infection induces a population of IL-17A⁺ CD4⁺ T cells that are tissue-restricted and antigen-specific, fulfilling CD4⁺ T_RM cell criteria.
• These CD4⁺ T_RM cells expand and serve as a primary source of IL-22 during secondary C. rodentium infection, preceding the T-cell response phase.
• FTY720 treatment confirmed the tissue-restricted nature of these cells, and they were shown to promote host defense.

Conclusions:

• Citrobacter rodentium infection establishes a population of CD4⁺ T_RM cells in the tissue.
• These CD4⁺ T_RM cells are critical for effective host defense against secondary bacterial infections.
• This study provides a model for studying CD4⁺ T_RM cell induction and function.